The present invention relates to a photothermographic material. In particular, the present invention relates to a photothermographic material for scanners, image setters and so forth, which is especially suitable for photographic art. More precisely, the present invention relates to a photothermographic material for photographic art, which shows high sensitivity, high image density (Dmax) and low fog and can provide images suitable for photographic art.
There are known many photosensitive materials having a photosensitive layer on a support, with which image formation is attained by light-exposing imagewise. Those materials include those utilizing a technique of forming images by heat development as systems that can contribute to the environmental protection and simplify image-forming means.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of photographic art from the standpoints of environmental protection and space saving. Therefore, development of techniques relating to photothermographic materials for photographic art is required, which materials enable efficient exposure by a laser scanner or laser image setter and formation of clear black images having high resolution and sharpness. Such photothermographic materials can provide users with simpler and non-polluting heat development processing systems which eliminate the use of solution-type processing chemicals.
Methods for forming images by heat development are described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Klosterboer, xe2x80x9cThermally Processed Silver Systems Axe2x80x9d, Imaging Processes and Materials, Neblette, 8th ed., compiled by J. Sturge, V. Walworth and A. Shepp, Chapter 9, p.279, (1989). Such photothermographic materials comprise a reducible non-photosensitive silver salt (e.g., silver salt of an organic acid), a photocatalyst (e.g., silver halide) in a catalytically active amount and a reducing agent for silver, which are usually dispersed in an organic binder matrix. While the photosensitive materials are stable at an ordinary temperature, when they are heated to a high temperature (e.g., 80xc2x0 C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image generated upon exposure. The silver produced from the reaction of the reducible silver salt in the exposed areas shows black color and provides contrast with respect to the non-exposed areas, and thus images are formed.
European Patent Publication (hereinafter referred to as EP-A) 762,196, Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 9-90550 and so forth disclose that high-contrast photographic property can be obtained by incorporating Group VII or VIII metal ions or metal complex ions of such a metal into photosensitive silver halide grains for use in photothermographic materials, or incorporating a hydrazine derivative into the photosensitive materials. Further, U.S. Pat. No. 5,545,515 discloses use of hindered phenols as a reducing agent and use of acrylonitrile compounds as an ultrahigh contrast agent.
Furthermore, there are also reported examples of use of phenol compounds as a reducing agent, which compounds have an amino group substituted with an electron withdrawing group as a substituent (e.g., sulfonamidophenol compounds). For example, as described in JP-A-49-80386, JP-A-5-257227 and JP-A-10-221806, there are known methods of individually utilizing 2,6-dichloro-4-benzenesulfonamidophenol, p-benzenesulfonamidophenol and so forth as a reducing agent. However, even use of these compounds cannot improve sensitivity and cannot solve the problems concerning change of photographic performance during storage of photosensitive materials (in particular, fog).
Accordingly, it has been desired to provide a photothermographic material for photographic art, which shows high sensitivity, high Dmax (maximum density) and low fog and can provide images suitable for photographic art.
The objects of the present invention are to solve the aforementioned problems of the prior art. That is, a first object to be achieved by the present invention is to provide a photothermographic material which shows high sensitivity, high Dmax (maximum density) and low fog, and can provide images suitable for photographic art, in particular, as a photothermographic material for photographic art, more specifically, a photothermographic material for scanners, image setters and so forth.
A second object to be achieved by the present invention is to provide a photothermographic material which can be prepared by coating of an aqueous system, which is advantageous in view of environment and cost.
The inventors of the present invention assiduously studied in order to achieve the aforementioned objects. As a result, they found that an excellent photothermographic material which provides the desired effects could be obtained by containing a particular bisphenol compound and a particular phenol compound on the image-forming layer side, and thus accomplished the present invention.
That is, the present invention provides a photothermographic material comprising at least (a) a photosensitive silver halide, (b) a reducible silver salt, (c) a reducing agent represented by the following formula (1), (d) a binder, and (e) a phenol compound represented by the following formula (2) on the same side of a support. 
In the formula (1), V1 to V8 each independently represent hydrogen atom or a substituent. L represents a bridging group consisting of xe2x80x94CH(V9)xe2x80x94 or xe2x80x94Sxe2x80x94. V9 represents hydrogen atom or a substituent. 
In the formula (2), R1 and R2 each independently represent hydrogen atom or a substituent. X1 to X3 each independently represent hydrogen atom or a substituent, provided that the substituents represented by X1 to X3 do not represent hydroxy group, and when the substituents represented by X1 to X3 are bonded to the phenol ring via nitrogen atoms, X1 to X3 represent a nitrogen-containing heterocyclic group or a group represented as xe2x80x94NHxe2x80x94C(xe2x95x90O)xe2x80x94R4 where R4 represents a substituent having 8-40 carbon atoms. The substituents represented by R1, R2 and X1 to X3 may be bound to each other to form a ring.
Preferably, the photothermographic material of the present invention further contains (f) a phthalazine compound represented by the following formula (3). 
In the formula (3), Y represents hydrogen atom or a monovalent substituent, and m represents an integer of 1 to 6. (Y)m means that 1-6 of Y independently exist on the phthalazine ring, and when m is 2 or more, adjacent two of Y may form an aliphatic ring, an aromatic ring or a heterocycle.
Preferably, in the formula (2), at least one of X1 to X3 is a halogen atom, an alkoxy group, an aryloxy group, a heteroaryloxy group, an alkylthio group, an arylthio group, a heterocyclylthio group or a nitrogen-containing heterocyclic group that binds to the phenol ring via nitrogen atom.
Preferably, the photothermographic material of the present invention further contains an ultrahigh contrast agent.
Preferably, the photothermographic material of the present invention is prepared by using an aqueous coating solution.
In the present specification, ranges indicated with xe2x80x9c-xe2x80x9d mean ranges including the numerical values before and after xe2x80x9c-xe2x80x9d as the minimum and maximum values.
The photothermographic material of the present invention has photographic properties suitable for photographic art, i.e., high sensitivity and high Dmax (maximum density) as well as low fog.